Steam turbines



Jan. 31, 1967 5. 000 3,301,529

STEAM TURBINES Filed May 11, 1965 2 Sheets-Sheet 1 F/GJ.

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wm's n c l-J5, ak'wmx TsoN United States Patent 3,301,529 STEAM TURBINES Basil Wood, Twickenham, England, assignor to Merz &

McLellan Services Limited, Newcastle upon Tyne, England, a company of Great Britain Filed May 11, 1965, Ser. No. 454,859 Claims priority, application Great Britain, May 12, 1964, 19,808/ 64 7 Claims. (Cl. 25376) This invention relates to steam turbines of substantially axial flow type having at least one stage liable to work with saturated steam, and is concerned with the reduction or erosion caused by water in the steam.

According to the present invention substantially all of the stator vanes of such a stag-e are provided, near their ends remote from the turbine axis, with a divertor constituted by a shoulder so inclined that its upstream end is nearer than its downstream end to the turbine axis, and facing upstream and away from the axis the shoulder being exposed to the flow of steam. While major benefit is expected to be derived from such a shoulder applied to the convex side of the vane it may also be provided on the concave side.

The shoulder may be afforded by a groove cut in the face of the stator vane, or by a step in its thickness, but in general it will be convenient to attach a rib to afford the shoulder, which can be done without reducing the strength of the vane. Such a rib may be provided by a wire or rod of circular, semi-circular, rectangular, triangular, or T-s-haped section. Alternatively it may be of channel or other hooked or overhanging section with the concavity facing upstream so as to tend to prevent water from flowing over the rib.

The rib may be secured to the vane by silver soldering, welding, brazing or rivetting or by the use of an adhesive such, for example, as an epoxy resin. To improve the fixing, the rib may be of a section offering an extended face to contact the vane for example of L section or T section. Again the rib may be built up in situ, for example by depositing a bead of weld metal or band of adhesive, such as epoxy resin.

The height of the rib may vary in accordance with the general scale of the blades, being commensurate with the diameter of droplets formed on the vanes but in any event it will be comparatively shallow in relation to the pitch of the stator vanes so as not to unduly interfere with the main steam fiow.

At its downstream end the rib or other shoulder may terminate at a radius with respect to the turbine axis greater than the tip radius of the following rotor blade. Alternatively it may lead into a drain channel through which the water is removed.

Various proposals have previously been made with a view to eliminating the erosion of turbine blades by wet steam. In steam turbines working within the saturated region it is known that water condenses during the expansion, and, as it passes through the later stages, causes damage to the moving blades as well as reducing the efficiency of the stage. The centrifugal effect of the moving blades tends to concentrate the water towards the outer periphery of the stage, and it is found that the most severe damage normally occurs in the moving blades in the few inches near the blade tips.

It has been proposed to provide drain passages such as slots intended to allow water thrown off radially to drain away to the condenser or feed heater before each of the later stator stages, but it appears that such drainage slots do not prevent a proportion of the water from crossing the gap between the rotor blades and the following stator vanes. On the one hand it may do so as a fine spray caused by splashing on the inner face of the cover "ice band or stator, or it may wet the upstream face of the diaphragm ring or vane carrier and form a film of water which is then drawn into the vane passages where it is dragged from the circumferential periphery by eddies or secondary flow in the steam.

Water reaching the upstream edge of the stator vanes by either of these methods tends to collect on the convex side of the stator vane and move slowly over it, collecting in pools and finally being shed from the downstream edge of the stator vane in the form of large droplets. While water which is finely divided in the form of a mist tends to travel at the same speed as the steam which is designed .to enter the rotor blades at a comparatively small relative velocity, the water in the form of large droplets has a comparatively low velocity so that its velocity relative to the rotor blades is correspondingly high, and it is believed that such large water droplets are mainly responsible for erosion damage to the rotor blades.

The rib or other divertor in accordance with the present invention is designed to prevent such water from dribbling over the surface of the stator vane in a direction inclined towards the turbine axis or at a substantially constant radius from the turbine axis. Due to the inclination of the divertor the water is deflected towards the outer periphery where it is discharged harmlessly either clear of the tips of the moving blades or through suitably placed slots or holes to a drain channel communicating with the condenser or feed heater.

The invention may be put into practice in various ways but certain specific embodiments will be described by way of example with reference to the accompanying drawings in which FIGURE 1 is an axial section through part of a steam turbine incorporating the invention FIGURES 2 to 5 are similar views of slightly modified arrangements FIGURE 6 is a section perpendicular to the longitudinal axis of a vane indicating the rib in accordance with the invention and FIGURES 7, 8, 9 and 10 are sections perpendicular to the axis of a rib showing different forms of crosssection of rib.

FIGURE 1 is an axial section through a portion of the last two stages of a typical wet steam turbine in the region of the tips of the rotor blades, and shows the rotor blades 11 and 12 of the last stage and the last stage but one respectively, and the corresponding stationary guide vanes 13 and 14. The guide vane 14 is supported by a diaphragm ring 16 whilst the guide vane 13 is supported by a diaphragm ring 17, the space to the right of the latter being in communication with the condenser. The diaphragm rings 16 and 17 are supported in the usual way by a portion of the turbine casing 18.

It will be appreciated that the turbine is substantially symmetrical about its horizontal centre line which is parallel to and far above the top edge of FIGURE 1.

In accordance with the present invention the guide vane 13 is provided on its convex face with a rib 20, and the guide vane 14 is provided With a similar rib 21. In each case the rib 20 or 21 is oblique so that its upstream end (to the left in FIGURE 1) is nearer to the axis than its downstream end. Accordingly any water dribbling over the convex surface of the guide vane in the region of its outer end will be collected and diverted by the rib to the extreme outer end of the downstream edge of the guide vane 13 or 14.

The diaphragm ring 17 is provided with .a notch 23 at the tail of each vane to drain such water away radially beyond the tips of the moving blades 11. It will be understood that the flow of such Water is urged largely by pressure difference or friction with moving steam rather than by gravity, so that flow against gravity is quite possible. Moreover the-vanes lie in a circle in a plane perpendicular to the plane of FIGURE 1 at various angles to the vertical in that plane and in some places gravity will assist drainage.

The diaphragm ring 16 of the penultimate stage has drain holes 24 one at each vane extending through it to allow water guided by the rib 21 to drain to a space 25 which is connected by a passage 26 to the space in communication with the condenser. Each drain hole 24 is of restricted section so as to prevent undue loss of steam or weakening of the ring. It is shown countersunk at its entry so as to assist water to drain readily into it. Moreover it is advantageously made as short .as practicable to reduce the flow resistance to flashing water which undergoes a great change in volume on encountering the lower pressure downstream.

FIGURE 2 shows an arrangement which is closely analogous to the penultimate stage of FIGURE 1 but employs a diaphragm ring of different section. In this case the passage 24 at each vane is replaced by a radial passage 30 communicating with an oblique passage 31 of larger cross-section.

FIGURE 3 is very similar to FIGURE 2 except that the parts are of different shape but corresponding parts bear the same reference numerals.

In FIGURE 4 a short drain passage 32 at each vane opens through the diaphragm ring into an annular space 33 formed in the diaphragm ring or its seating or partly in one and partly in the other. This annular space is in turn vented through larger passages 34 to the downstream space 35 or to the condenser.

FIGURE shows a further arrangement in which a diaphragm ring is of composite construction with an inner part 36 having a short drain passage 37 at each vane extending through it and opening into a hollow annular space 38 within the outerpart of the diaghragm ring 39, whilst the annular space 38 is vented through a passage or passages 40 to the downstream space 41 or to the condenser.

The precise form of the ribs 20 and 21 may vary. FIGURE 6 shows one example in which the rib is hooked over the upstream edge 42 of the Vane as shown at 43.

FIGURES 7 to show various forms of cross-section which the rib may assume. Thus FIGURE 7 shows a rib 44 of T section, FIGURE 8 shows a rib 45 of round section, FIGURE 9 shows a rib 46 of half round section, and FIGURE 10 shows a rib 47 of channel section. In the case of a rib such as a rib 47 of channel or other hooked or overhanging section it is preferred that the concavity should face upstream, that is to say to the left and downwards or radially outwards as viewed in FIG- URE 1, so as to tend to prevent water from flowing over the rib.

What I claim as my invention and desire to secure by Letters Patent is:

l. A steam turbine of substantially axial fiow type including a rotor having rotor blades and a stator having stator vanes including at least one stage which is liable to work with saturated steam, a water divertor for each stator vane of the said stage, said divertor comprising a shoulder on the body of said vane adjacent the end remote from the turbine axis, said shoulder being shallow in relation to the pitch of the stator vanes, said shoulder being so inclined that its upstream end is nearer than its downstream end to the turbine axis, said shoulder being positioned on the upstream side of said vane so as to face upstream and away from said turbine axis, whereby said shoulder is operative to divert away from said axis any water deposits creeping along said vane while allowing the useful steam to pass over the same for further use.

2. A turbine as claimed in claim 1 in which said upstream side is convex.

3. A turbine as claimed in claim 1 in which said shoulder comprises a raised rib attached to said upstream side of said vane.

4. A turbine as claimed in claim 3 in which the rib is in the form of a wire.

5. A turbine as claimed in claim 3 in which said rib includes an overhanging section, said section and the blade forming a cavity facing upstream so as to prevent water from flowing over said rib.

6. A turbine as claimed in claim 1 in which is provided a drain channel opening at the downstream end of said shoulder, whereby said water is removed from said turbine.

7. A turbine as claimed in claim 1 in which the upstream end of said shoulder begins at .a radius with respect to the turbine axis less than the tip radius of the preceding rotor blades.

References Cited by the Examiner UNITED STATES PATENTS 1,696,002 12/1928 Hanzlik 253-76 1,736,612 11/1929 Lysholm 253-76 1,834,451 12/1931 Frey 25376 2,121,645 6/1938 Warren 253-76 2,399,009 4/1946 Doran 25376 FOREIGN PATENTS 164,297 12/1933 Switzerland.

EDGAR W. GEOGHEGAN, Primary Examiner. EVERETTE A. POWELL, JR., Examiner, 

1. A STEAM TURBINE OF SUBSTANTIALLY AXIAL FLOW TYPE INCLUDING A ROTOR HAVING ROTOR BLADES AND A STATOR HAVING STATOR VANES INCLUDING AT LEAST ONE STAGE WHICH IS LIABLE TO WORK WITH STATURATED STEAM, A WATER DIVETOR COMPRISING A STATOR VANE OF THE SAID STAGE, SAID DIVERTOR COMPRISING A SHOULDER ON THE BODY OF SAID VANE ADJACENT THE END REMOTE FROM THE TURBINE AXIS, SAID SHOULDER BEING SHALLOW IN RELATION TO THE PITCH OF THE STATOR VANES, SAID SHOULDER BEING SO INCLINED THAT ITS UPSTREAM END IS NEARER THAN ITS DOWNSTREAM END TOE THE TURBINE AXIS, SAID SHOULDER BEING POSITIONED ON THE UPSTREAM SIDE OF SAID VANE SO AS TO FACE UPSTREAM AND AWAY FROM SAID TURBINE AXIS, WHEREBY SAID SHOULDER IS OPERATIVE TO DIVERT AWAY FROM SAID AXIS ANY WATER DEPOSITS CREEPING ALONG SAID VANE WHILE ALLOWING THE USEFUL STEAM TO PASS OVER THE SAME FOR FURTHER USE. 